Aqueous dust suppression fluid and a method for suppressing dust

ABSTRACT

An aqueous, coal dust suppression fluid comprising one or more surfactants and at least one high terpene-containing natural oil. The coal dust suppression fluid can be used in a formulation of water dosed with the aqueous dust suppression fluid for the abatement of coal dust. A method is described for the abatement of coal dust using the formulation.

CO-PENDING APPLICATION

This application is a continuation application of allowed applicationSer. No. 07/944,089 filed Sep. 11. 1992 now U.S. Pat. No. 5,330,671.

BACKGROUND OF THE INVENTION

The invention relates to aqueous, coal dust suppression fluids, andformulations for the abatement of coal dust containing water dosed withdust suppression fluids. Furthermore, the invention relates to methodsfor the abatement of coal dust.

Dust suppression is the reduction of the extent to which finely dividedsolid particulate material becomes suspended in the air. A variety ofmaterials such as coal, sulfur, phosphate, clay, and other finelydivided ores and minerals, generate dust in transfer and handlingoperations during mining, transportation, storage, and use.

Dust is a particularly severe safety and health hazard in coal mining,handling, and storage operations. Coal often chips into small fragmentsby the action of wind and rain, frictional movement due to motion intransit, and abrasion in handling. Respirable coal dust has a particlesize of less than about 10 microns and its inhalation can lead topneumoconiosis, i.e., "black lung disease". Also, dust explosions due tospontaneous combustion may occur when the dust is confined to a smallair space such as in coal mining operations.

It is known to suppress coal dust in mines by spraying with variousaqueous systems containing chemical additives to improve workingconditions and reduce the toxicological risks and explosion hazards. Forexample, U.S. Pat. No. 4,425,252 describes a method to abate coal dustusing an anionic surfactant, preferably sodium dodecyclbenzenesulphonate and a nonionic surfactant, preferably a polyethoxylatednonylphenol, in an aqueous formulation. The method comprises sprayingthe coal dusty area with a formulation comprising water containing up to0.1% by weight of the mixture of the anionic surfactant, i.e., a watersoluble salt of an alkyl aryl sulfonic acid and nonionic surfactanthaving an HLB of from 10 to 16. Optimally, the mixture contains one ormore cosolvents generally of the class of alkylene glycol monoalkylethers, C₂ to C₅ alkanols and mixtures thereof.

Furthermore, several techniques have been developed utilizing foamablecompositions for suppressing coal dust. For example, U.S. Pat. No.4,551,261 describes a foam comprising water, a foaming agent, and anelastomeric water insoluble polymer. A variety of anionic and nonionicsurfactants and detergent wetting agents are described as useful foamingagents, and a variety of elastomeric and water insoluble syntheticorganic polymer binders are described as useful elastomeric waterinsoluble polymers.

U.S. Pat. No. 4,971,720 describes a method for suppressing dust processemissions. The method utilizes a foaming agent which may be a low salttolerant surfactant selected from salts of fatty acids, alkyl sulphates,and alkyl aryl sulphonates.

U.S. Pat. No. 4,561,905 describes a coal dust suppression mixture ofoil, water and a surfactant in the form of an emulsion that is dilutedand foamed. The foam is then sprayed into a falling mass of coal. Theoils suitable for use are described as heavy process oils and includeasphalt dissolved in a moderately heavy oil, residual flush oils orrelatively high viscosity fuel oil. The preferred oils have a viscosityin the range of from approximately 600 to 7,000 SUS at 38° C., a pourpoint in the range of approximately -18 to 21° C., a molecular weight ofat least 300 and a boiling point of at least 204° C.

Thus, various techniques have been developed to suppress coal dust, andmany of the techniques are effective for reducing that dust. However,there is still a need for improvement in coal dust suppression, and manyof the prior techniques were developed without a need to addressproblems associated with modern coal mining practices.

SUMMARY OF THE INVENTION

Accordingly, it is the primary object of the invention to provide aneffective, novel coal dust suppression fluid, which also effectivelyaddresses certain problems associated with modern coal mining practices.For example, most modern, state-of-the-art, continuous coal minesutilize scrubbers which tend to clog. Thus, there is a need for amaterial which not only effectively reduces airborne dust, but alsoeffectively assists in keeping spray nozzles and scrubber screens cleanand unclogged. In addition, coal suppression fluids often have secondaryuses and are frequently circulated through mine equipment underground asa heat exchange fluid. However, water jackets on that equipment tend toaccumulate mineral deposits such as calcium deposits, drasticallyreducing cooling efficiency. Hence, it is a further object of theinvention to provide a coal dust suppression fluid which increasescooling efficiency when used as a heat exchange fluid by maintaining thewater jackets on the equipment underground free of mineral deposits suchas calcium deposits.

Many of the chemical additives used in coal dust suppression fluids arealso very expensive. It is therefore another object of the invention toprovide a coal dust suppression fluid which reduces the need for costlychemical additives. Furthermore, many of the chemicals used in coal dustsuppression are themselves toxic to humans to some degree, anddestructive of the environment. Thus, another object of the invention isto provide a coal dust suppressing fluid which is less toxic to humansand is environmentally acceptable thereby reducing process watercontamination; water which ultimately will find its way to localstreams, rivers and lakes.

Another problem associated with the prior art is the vast amount ofprocess water which is necessary for coal dust suppression. Whileprocess water is dosed with various aqueous solutions containingchemical additives to assist in dust reduction, the amount of actualprocess water used remains very high. It is thus even another object ofthe invention to provide a coal dust suppression fluid which actuallyreduces the amount of process water needed for dust suppression.

The aforementioned and other objects of the invention can be obtained bythe invention. The invention provides a novel, aqueous, coal dustsuppression fluid comprising one or more surfactants and at least onehigh terpene-containing natural oil. Another aspect of the inventionrelates to a formulation for the abatement of coal dust comprising waterdosed with the aforementioned aqueous dust suppression fluid. Evenanother aspect of the invention relates to a method for the abatementcoal dust using the formulation.

The novel coal dust suppression fluid of the invention is very effectivefor suppressing airborne dust when used in a formulation for theabatement of coal dust. Furthermore, the fluid can effectively assist inkeeping spray nozzles and scrubber screens clean and unclogged. Inaddition, the coal dust suppression fluid can increase coolingefficiency when used as a heat exchange fluid by continuously clearingmineral deposits such as calcium deposits from water jackets on theunderground equipment. Also, the coal dust suppression fluid can reducethe need for costly chemical additives, and can provide a coal dustsuppression fluid which is less toxic to humans and is environmentallyacceptable. When process water is dosed with the coal dust suppressionfluid of the invention, it has also been found that the fluid canactually reduce the amount of process water needed for coal dustsuppression.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, the invention relates to a novel, aqueous, coal dustsuppression fluid comprising one or more surfactants and at least onehigh terpene-containing natural oil. Process water can be dosed with thefluid to provide a coal dust suppression formulation. Coal dust iscontacted with the formulation for the abatement of coal dust.

High terpene-containing natural oil as used herein is defined as thosenatural oils having a terpene content of at least 50%. It is preferablethat the high terpene-containing natural oil contain at least 90%terpenes.

Suitable high terpene-containing natural oils include the citrus peeloils, preferably orange oil, grapefruit oil and lemon oil. Of these,orange oil is the most preferred as it contains about 90 to 94% terpenesand is very abundant in certain parts of the world. Pine oil is also auseful high terpene-containing natural oil.

Generally, the coal dust suppression fluid will contain about 1 to about15% by weight high terpene-containing natural oils, preferably about 8to about 12% by weight, and more preferably about 8 to about 10% byweight. Naturally, the amount of high terpene-containing natural oilswill depend upon the amount of terpenes in the oil. For example, in thecase of the preferred embodiment, orange oil, the oil can be added in anamount of from 1 to about 15% by weight, although it is preferably addedin an amount of about 8 to about 10% by weight.

While not wishing to be bound by theory, it is believed that theterpenes in the natural oils provide the mechanism for obtaining many ofthe objects of the invention. For example, the terpenes are believed tobreak up oily (fatty) deposits on the coal that tend to clog spraynozzles and scrubber screens. Furthermore, the terpenes are believed tobreak up fatty layers on coal particles allowing the water droplets tobetter wet the coal particles.

In addition, because the high terpene content oils are natural oils,environmentally acceptable products are being used to dose the processwater, thereby reducing process water contamination. With respect to atleast orange oil, it is also believed that this oil in combination withcleaned coal particles act as a liquid ionizer. This is seen from areduction in total dissolved solids and suspended solids which remain inthe process water.

The aqueous, coal dust suppression fluid of the invention also containsat least one surfactant. Generally, conventional surfactants used incoal dust abatement can be used such as anionic and nonionicsurfactants. Preferred are anionic surfactants such as salts of fattyacids, alkyl sulphates, alkyl ether sulphonates, and alkyl arylsulphonates. Examples of preferred surfactants include sodiumdodecylbenzene sulphonate, sodium lauryl ether sulphate and salts suchas sodium salts of secondary alkane sulphonates (e.g., Hostaspun SAS 60marketed by Hoechst).

Also, the use of ethoxylated nonylphenols with 8-10 moles of ethyleneoxide and ethoxylated octylphenols with 8-10 moles of ethylene oxide,(e.g., alkylaryl polyglycol ether N9), in the fluid are preferred.

Generally, a large portion of the aqueous coal dust suppression fluidwill comprise surfactants. For example, the fluid can contain up toabout 40% by weight surfactant(s), preferably from about 15 to about 25%by weight surfactant(s), and more preferably about 20 to about 22% byweight.

The coal dust control composition of the invention may contain a varietyof additives such as antioxidants and preservatives. An example of asuitable antioxidant is BHT (2,6-di-tert-butyl-para-cresol). Theantioxidant(s) may be added to the composition in an amount of 0.01 to1% by weight, preferably 0.08 to 0.12% by weight.

Examples of suitable preservatives include formaldehyde, methylparaben,propylparaben, borax, and mixtures thereof. The preservatives may beadded to the composition in an amount of 0.5 to 5% by weight, preferably0.8 to 1.2% by weight.

Since the coal dust suppression fluid is an aqueous composition, thebalance of the composition will be water. Typically, the fluid willcontain from about 66 to about 70% by weight water.

An example of an effective coal dust control fluid comprises 10.95%sodium dodecyl benzene sulphonate, 5.1% sodium lauryl ether sulphate,9.1% cold pressed orange oil, 3.5% alkyl aryl polyglycolether N9, 1.4%of the sodium salt of a secondary alkane sulphonate, 1.0% formaldehyde,and 0.1% of an antioxidant; with the balance being water (allpercentages are by weight).

In operation, process water will be dosed with the coal dust suppressionfluid to provide a coal dust abatement formulation. Typically, processwater can be dosed with the fluid at a weight ratio of about 3000:1 upto about 15000:1 (water/fluid) to provide an effective formulation forthe reduction in airborne dust. More preferably, process water can bedosed with the fluid at a weight ratio of about 7000:1 up to about9000:1.

The dust suppression fluid can be injected into a main column of processwater pumped into the coal mine. The process water can be pumped by anelectronically controlled pump. The metering pump can be controlled by aflow meter and control box measuring the amount of flow. The dosedprocess water can then be directed as needed, to various parts of themine for dust suppression.

Another aspect of the invention provides a mechanism for dewateringcoal. Once coal has been mined, it is typically sent to a preparationplant. In preparation plants, coal is sorted by various methods, such asby changing the specific gravity of fluids in which the coal is dumped.By raising or lowering of the specific gravity of those fluids, variousqualities of coal can be sorted by the coal specific gravity. After thecoal has been sorted, it is washed.

Among other things, process water is also removed from the coal in thepreparation plants. The removal of water from the coal product in thepreparation plant is one of the most economically significant steps incoal cleaning. That is, efficient dewatering is critical to ensurecontract compliance, minimize transportation costs, and reduce coalhandling problems, especially with respect to water freezing in storagevessels and rail cars.

There have been many mechanical techniques such as filtration andcentrifugation which have been used to remove process water inpreparation plants. Also, chemical techniques have been used to dewatercoal. For example, surface active agents have been used to reduce watersurface tension and enhance water removal from coal products.

The present invention unexpectedly provides a novel composition whichcan enhance water removal from mined coal products. As a chemicaltechnique for removing water from coal at a preparation plant, thecomposition can be used, for example, in disc or drum filtrationapplications by feeding the composition directly to a slurry entering afilter vat. Or, a solution of the composition can be sprayed directly ona filter cake. Centrifugal dryer feed can be readily treated by sprayinga solution of the composition onto the coal as it discharges fromdewatering screens, etc.

In another and preferred embodiment of the invention, the compositioncan be added to the wash water. As the wash water will then have asubstantially reduced surface tension, less will remain with the coalafter washing. For example, by using this technique 96%, instead of 94%coal per ton of freight could be obtained for larger sizes, and 88% coalrather than 84% coal for fine coal. In a broad sense, by dosing washwater by about 7 to 50 grams per metric ton of coal to be washed withthe composition according to the invention a 30 to 70% reduction inwater content can be provided.

As a particularly effective embodiment of the invention, the compositioncan be used both in a preparation plant for dewatering applications, andfor coal dust suppression. For example, dust abatement water dosed withthe dust suppression fluid of the invention can also be used inpreparation plant dewatering if run-off water is used.

While the invention has been described above with respect to certainparticular embodiments thereof, numerous other forms and modificationswill be apparent to those skilled in the art. The appended claims andthe invention generally should be construed as covering all such obviousforms and modifications which are within the true spirit and scope ofthe invention.

What is claimed is:
 1. An aqueous composition formulated for thesuppression of particulate material including dust comprising one ormore surfactants in an amount, of from about 15 to about 25% by weightselected from salts of fatty acids, alkyl sulphates, alkyl ethersulphonates and alkyl aryl sulphonates, and at least one high terpenecontaining natural oil containing at least 90% terpenes and selectedfrom one or more citrus peel oils, said fluid comprising amounts of saidsurfactant(s) and high terpene containing natural oil(s) effective incombination for dust suppression.
 2. An aqueous fluid according to claim1 wherein the citrus peel oil (s) is/are selected from orange oil, lemonoil and grapefruit oil.
 3. An aqueous fluid according to claim 2 whereinthe aqueous dust suppression fluid contains orange oil.
 4. An aqueousfluid according to claim 1, said fluid comprising sodium dodecylbenzenesulphonate and sodium lauryl ether sulphate.
 5. An aqueous fluidaccording to claim 1 further comprises at least one antioxidant or atleast one preservative, or both.
 6. A formulation for the abatement ofdust comprising water dosed with an aqueous dust suppression fluidaccording to claim 2, said water being dosed with the aqueous dustsuppression fluid in an amount effective for the abatement of dust.
 7. Amethod for the suppression of particulate material including dustcomprising contacting dust with a formulation for the abatement of dustcomprising water dosed with an aqueous, dust suppression fluid in anamount effective for the abatement of dust, said aqueous, dustsuppression fluid comprising one or more surfactants and at least onehigh terpene-containing natural oil containing at least 90% terpenes andselected from one or more citrus peel oils, said fluid comprisingamounts of said surfactant(s) and high terpene-containing natural oil(s)effective in combination for dust suppression.
 8. A method forsuppressing dust according to claim 7, said surfactant(s) being selectedfrom salts of fatty acids, alkyl sulphates, alkyl ether sulphonates andalkyl aryl sulphonates.
 9. A method for suppressing dust according toclaim 8, said fluid comprising sodium dodecylbenzene sulphonate andsodium lauryl ether sulphate.
 10. A method for suppressing dustaccording to claim 8, said fluid comprising from about 15 to about 25%by weight surfactant(s).
 11. A method for suppressing dust according toclaim 7, said fluid comprising sodium dodecylbenzene sulphonate, sodiumlauryl ether sulphate and orange oil.
 12. A formulation for theabatement of particulate material including dust comprising water dosedwith an aqueous, dust suppression fluid in an amount effective for theabatement of dust, said aqueous dust suppression fluid comprising one ormore surfactants selected from salts of fatty acids, alkyl sulphates,alkyl ether sulphonates and alkyl aryl sulphonates, and at least onehigh terpene-containing natural oil containing at least 90% terpenes andselected from one or more citrus peel oils, said fluid comprisingamounts of said surfactant(s) and high terpene containing natural oil(s)effective in combination for dust suppression.
 13. A formulation for theabatement of particulate material including dust comprising water dosedwith an aqueous, dust suppression fluid in an amount effective for theabatement of dust, said aqueous, dust suppression fluid comprisingsodium dodecylbenzene sulphonate, sodium lauryl ether sulphate andorange oil in amounts effective in combination for dust suppression, andsaid dust suppression fluid further comprising an antioxidant, apreservative, or both.
 14. An aqueous composition formulated for thesuppression of particulate material including dust comprising sodiumdodecylbenzene sulphonate, sodium lauryl ether sulphate, and at leastone high terpene-containing natural oil containing at least 90% terpenesand selected from one or more citrus peel oils, said fluid comprisingamounts of sodium dodecylbenzene sulphonate, sodium lauryl ethersulphate, and high terpene-containing natural oil(s) effective incombination for dust suppression.